The objective of Project 4 is to determine the principal fate and transport processes for the release, mobility, persistence, and possible pathways of mixtures of organic contaminants toward potential exposures and/or remediation zones in karst groundwater systems. The Project will use Dl(2- ethylhexyl) phthalate (DEHP) as a model semipolar organic and trichloroethylene (TCE) as a model nonpolar organic. The project will determine the major mechanisms influencing the fate and transport of DEHP and TCE in karst groundwater characterized by variable conduit and/or diffusion dominated flow;assess the effect of trapped and mobile non-aqueous TCE on the fate and transport of dissolved DEHP;assess potential contamination pathways and exposure through the karstic groundwater system in northern Puerto Rico;and explore the mechanisms for potential release and leaching of DEHP contaminants from unlined landfills into karst groundwater systems. Specific alms will be attained through defined experimental activities, which Involve data evaluation and integration at the hydrogeophysical system level and physical modeling of potential contaminant sources and fate and transport processes at the laboratory-scale level.